<?php
class LtStoreMemory implements LtStore
{
    protected $stack;
    public function add($key, $value)
    {
        if (isset($this->stack[$key])) {
            return false;
        } else {
            $this->stack[$key] = $value;
            return true;
        }
    }
    public function del($key)
    {
        if (isset($this->stack[$key])) {
            unset($this->stack[$key]);
            return true;
        } else {
            return false;
        }
    }
    public function get($key)
    {
        return isset($this->stack[$key]) ? $this->stack[$key] : false;
    }
    /**
     * key不存在返回false
     * 
     * @return bool 
     */
    public function update($key, $value)
    {
        if (!isset($this->stack[$key])) {
            return false;
        } else {
            $this->stack[$key] = $value;
            return true;
        }
    }
}
